Methods and apparatuses to provide a tunable chromatic dispersion compensator

Abstract

Various methods, systems and apparatuses in which a chromatic dispersion compensation module includes an input fiber, an output fiber, a lens, and an etalon resonator. The input fiber has a first core with a center. The output fiber has a second core with a center. The input fiber is adjacent to the output fiber. The spacing between the center of the first core and the center of the second core is affixed to less than one hundred and twenty microns. The input fiber routes an optical signal to lens. The lens routes the optical signal to the etalon resonator. The etalon resonator has reflectors with fixed reflectivity and a variable optical length to induce a wavelength-dependent delay into the optical signal. The a etalon resonator routes the optical signal to the output fiber through the lens.

We claim:  
     
       1. An apparatus, comprising: 
       a chromatic dispersion compensation module that includes  
       an input fiber having a first core with a center;  
       an output fiber having a second core with a center, the input fiber is adjacent to the output fiber, spacing between the center of the first core and the center of the second core is affixed to less than one hundred and twenty microns;  
       a lens, the input fiber to route an optical signal to the lens;  
       an etalon resonator having reflectors with fixed reflectivity and a variable optical length to induce a wavelength-dependent delay into the optical signal, the lens to route the optical signal to the etalon resonator; the etalon resonator to route the optical signal to the output fiber through the lens; and  
       two or more chromatic dispersion compensation modules cascadedly connected together.  
     
     
       2. The apparatus of  claim 1 , wherein the lens is a collimating lens. 
     
     
       3. The apparatus of  claim 1 , wherein the lens is approximately a focal length away from an output of the input fiber. 
     
     
       4. The apparatus of  claim 1 , wherein the input fiber and the output fiber comprise a pair of fibers, each fiber having an approximately flat surface and affixed to the other fiber at the approximately flat surface. 
     
     
       5. The apparatus of  claim 1 , wherein the input fiber and the output fiber comprise a pair of thermally expandable core (TEC) collimating fibers. 
     
     
       6. The apparatus of  claim 1 , further comprising: 
       a first micro lens coupled to an output of the input fiber; and  
       a second micro lens coupled to an input of the output fiber.  
     
     
       7. The apparatus of  claim 1 , further comprising: 
       a first prism interposed between the input fiber and the lens; and  
       a second prism interposed between the output fiber and the lens.  
     
     
       8. The apparatus of  claim 1 , wherein the spacing between the center of the first core and the center of the second core is affixed to a value between the range of fifty to one hundred and twenty microns. 
     
     
       9. The apparatus of  claim 1 , wherein the input fiber and the output fiber comprise a pair of fused fibers, each fiber having a tapered cladding, the first core of the input fiber positioned relative to the second core of the output fiber to possess a figure of merit of less than two tenths. 
     
     
       10. The apparatus of  claim 1 , wherein the variable optical path of the etalon resonator is tuned to a center wavelength by solely changing temperature of that etalon resonator. 
     
     
       11. The apparatus of  claim 1 , wherein the variable optical path of the etalon resonator is tuned to a center wavelength by solely changing strain on that etalon resonator. 
     
     
       12. The apparatus of  claim 1 , wherein the variable optical path of the etalon resonator is tuned to a center wavelength by solely changing spacing between a front reflector and a back reflector of the etalon resonator. 
     
     
       13. The apparatus of  claim 1 , wherein the chromatic dispersion compensation module has an operating wavelength range greater than twenty nanometers. 
     
     
       14. The apparatus of  claim 1 , wherein the chromatic dispersion compensation module has a figure of merit ratio of less than one tenth. 
     
     
       15. The apparatus of  claim 1 , wherein the chromatic dispersion compensation module has a figure of merit ratio of less than five one hundredths. 
     
     
       16. An apparatus Tho apparatus of  claim 1 , comprising: 
       a chromatic dispersion compensation module that includes  
       an input fiber having a first core with a center;  
       an output fiber having a second core with a center, the input fiber is adjacent to the output fiber, spacing between the center of the first core and the center of the second core is affixed to less than one hundred and twenty microns;  
       a lens, the input fiber to route an optical signal to the lens; an etalon resonator having reflectors with fixed reflectivity and a variable optical length to induce a wavelength-dependent delay into the optical signal, the lens to route the optical signal to the etalon resonator: the etalon resonator to route the optical signal to the output fiber through the lens, wherein each etalon resonator connects to a temperature control device.  
     
     
       17. The apparatus of  claim 16 , wherein the reflectors include a front reflector having a fixed reflectively between two and sixty percent. 
     
     
       18. The apparatus of  claim 16 , wherein the chromatic dispersion compensation modulo has an operating wavelength range greater than twenty nanometers. 
     
     
       19. The apparatus of  claim 16 , wherein the input fiber and the output fiber comprise a pair of fibers, each fiber having an approximately flat surface and affixed to the other fiber at the approximately flat surface. 
     
     
       20. An apparatus comprising: 
       a chromatic dispersion compensation module that includes  
       an input fiber;  
       an output fiber, the input fiber adjacent to the output fiber;  
       a lens, the input fiber to route an optical signal to the lens;  
       a first etalon resonator having reflectors with wavelength-dependent reflectivity and a variable optical length to induce a wavelength-dependent delay into the optical signal, the lens to route the optical signal to the first etalon resonator; the first etalon resonator to route the optical signal to the output fiber through the lens; and  
       a temperature control device affixed to the first etalon resonator to control temperature of the first etalon resonator independent of any other etalon resonator; and  
       a series of cascadedly connected etalon resonators, wherein each etalon resonator in the series of etalon resonators has a front reflector with a different reflectivity in order to optimize a flatter dispersion slope and a higher magnitude of dispersion induced on each wavelength per etalon.  
     
     
       21. The apparatus of  claim 20 , wherein at least one of the reflectors with wavelength dependent reflectivity comprises a fiber Bragg grating. 
     
     
       22. The apparatus of  claim 20 , wherein at least one of the reflectors wavelength dependant reflectivity comprises a mirror having dielectric layers that produce a wavelength dependant response. 
     
     
       23. The apparatus of  claim 20 , wherein the temperature control device maintains temperature of the first etalon resonator above ambient temperature. 
     
     
       24. The apparatus of  claim 20 , wherein 
       the input fiber has a first core with a center;  
       the output fiber has a second core with a center, the input fiber is adjacent to the output fiber, spacing between the center of the first core and the center of the second core is affixed to less than one hundred and twenty microns.  
     
     
       25. The apparatus of  claim 20 , wherein the reflectors include a front reflector having a wavelength dependant reflectivity between two and sixty percent. 
     
     
       26. An system, comprising: 
       a series of cascaded chromatic dispersion compensation modules, a first chromatic dispersion compensation module that includes  
       an input fiber having a first core with a center;  
       an output fiber having a second core with a center, the input fiber adjacent to the output fiber, spacing between the center of the first core and the center of the second core is affixed to less than one hundred and twenty microns;  
       a lens, the input fiber to route an optical signal to the lens; and  
       a first etalon resonator having reflectors with fixed reflectivity and a variable optical length to induce a wavelength-dependent delay into the optical signal, the lens to route the optical signal to the first etalon resonator; the first etalon resonator to route the optical signal to the output fiber through the lens.  
     
     
       27. The system of  claim 26 , further comprising: 
       a temperature control device affixed to the first etalon resonator to control temperature of the first etalon resonator independent of any other etalon resonator.  
     
     
       28. The system of  claim 26 , wherein at least two or more etalon resonators in the series of chromatic dispersion compensation modules has a front reflector with a different reflectivity in order to optimize a flatter dispersion slope and a higher magnitude of dispersion induced on each wavelength per etalon. 
     
     
       29. The system of  claim 26 , wherein the series of cascaded chromatic dispersion compensation modules includes a first set of etalon resonators and a second set of etalon resonators to adjust a slope of the dispersion compensation across a passband of wavelengths independently of a total amount of dispersion compensation induced across the passband of wavelengths. 
     
     
       30. An apparatus, comprising: 
       means for inducing wavelength-dependent delays in to an optical signal;  
       means for collimating the optical signal;  
       means for routing the optical signal through a series of an etalon resonators in a first chromatic dispersion module;  
       means for tuning the resonant center wavelength of the etalon resonator by adjusting optical path length of the etalon resonator;  
       means for routing, via a non-normal angle of incidence, the optical signal to an output, wherein the non-normal angle of incidence incurs a figure of merit of less than two tenths; and  
       means for routine the optical signal through a second chromatic dispersion module in series with the first chromatic dispersion module.  
     
     
       31. The apparatus of  claim 30 , further comprising: 
       means for adjusting an optical path length of the etalon resonator while maintaining the fixed reflectivity of reflectors in that etalon resonator.